Electrostatic atomizers are devices for applying atomized and electrically charged paint onto work pieces due to electrostatic attraction under an electrostatic field generated by application of a high voltage. Because they use such a high voltage, leakage of the high voltage is one of important issues of electrostatic atomizers and electrostatic coating systems including such electrostatic atomizers.
In Japanese Patent Laid-open Publication No. JP H10(1998)-109054, it is pointed out that a deposition of paint on the outer surface of an electrostatic atomizer may act to bring about a high voltage leak or, when fragments of the deposit of paint from the outer surface of the atomizer happen to adhere onto a work, they degrade the coating quality of the work. As a countermeasure with this problem, this publication proposes to detect a leak current by locating a grounded electrode at a position apart from the front end of the electrostatic atomizer, that is, at a position apart from a high voltage application electrode (like a bell head, for example) for electrostatically charging the paint particles.
The above proposal is effective to alleviate the problem caused by deposition of paint onto outer surfaces of electrostatic atomizers. Most electrostatic atomizers have the characteristics that, if the atomizer has been contaminated, a leak current exhibits a preliminary rise before the contamination heavily increases. Therefore, the preliminary rise of the leak current may be detected to use it as a factor for a countermeasure against leakage of current such as issuing an alarm, for example.
In Japanese Patent Laid-open Publication No. JP 2002-186884, it is proposed to solve the problem caused by a deposition of paint on outer surfaces of an electrostatic atomizer by integrating the magnitude of a current or voltage in a high voltage application path for supplying a high voltage to a high voltage application electrode to issue an alarm to call operator's attention when the integrated value exceeds a predetermined threshold.
According to Japanese Patent Laid-open Publication No. JP H10-109054, the grounded electrode is provided on an outer surface of an electrostatic atomizer as explained above. This publication further proposes the use of a ring-shaped grounded electrode provided directly on an electrically insulative outer housing of the electrostatic atomizer or in a location radially outwardly apart from the outer housing.
However, the additional use of the grounded electrode raises the cost, and also requires a change of design of the outer housing of the electrostatic atomizer.